The present invention relates to a spinal implant apparatus and a method of using that apparatus to treat a spine disorder. More particularly, the present invention relates to an implant apparatus, which includes a steerable spacer and a manipulation device or positioning tool, and a method for using the positioning tool to position the spacer at a desirable position at the anterior region of a vertebra. Further, the present invention relates to an intervertebral spacer arranged for selectable steerage to a location of interest between adjacent vertebrae, and a mechanism to manipulate or alter the apparatus in an off-axis manner.
Back pain can be caused by any one of several problems that affect the intervertebral discs of the spine. These problems include, for example, degeneration, bulging, herniation, thinning of a disc, or abnormal movement, and the pain that is experienced generally is attributable to friction or pressure that inevitably occurs when one adjacent vertebra exerts uneven pressure, or when both adjacent vertebrae exert such pressure, on the disc. Back pain may also be attributed to neural element injury.
Whenever an individual suffers from a disc problem, a typical remedy is to perform interbody, intervertebral, cervical, thoracic, or lumbar fusion (all generically referred to herein as “IF”) surgery on the patient for the purpose of fusing together the two vertebrae that flank the defective disc to form a single, solid bone mass. Existing IF techniques generally involve removing the offending disc from the patient, adding bone graft material into the interbody space between the flanking vertebrae, and inserting a spinal implant device into that space to hold the graft material in place and to support the flanking vertebrae while solid bone mass forms.
Existing IF techniques fail to enable fine positioning of an implant device with respect to the vertebrae. A brief discussion of the basic anatomy of the human spine, and specifically, the lumbar vertebrae of the spine, will help better illustrate this limitation. FIG. 1 is a partial representation of the lumbar region of a human spine, in which an intervertebral disc 10 is arranged between a superior vertebra 20 and an inferior vertebra 30. Specifically, disc 10 is positioned between a bottom surface 21 of superior vertebra 20 and a top surface 31 of inferior vertebra 30. FIG. 2 is a top view of inferior vertebra 30, which includes top surface 31 of a vertebral body 32. Vertebral body 32 is formed by a cortical rim 33, which is a dense, hard shell that is formed by compact bone, and an end plate portion 34 formed by much softer and less compact end plate material, or cancellous bone.
Referring to FIG. 3, existing IF procedures, including those associated with the lumbar region, involve positioning at least one spinal implant 50 so that it is substantially centered between end plate portion 34 of inferior vertebra 30 and an end plate portion 24 on bottom surface 21 of superior vertebra 20. Such positioning of implant 50 does not promote lordosis. Further, in this position, implant 50 tends to depress upon, or even become embedded in, end plate portion 34 of inferior vertebra 30 and/or end plate portion 24 of superior vertebra 20. This settling of implant 50 is referred to as subsidence, during which the vertebrae-supporting properties of implant 50 are reduced or eliminated. The result may be less than desirable coronal and/or sagittal alignment of the spine.
Existing IF procedures are further limited in other ways. During IF surgery, the surgeon must navigate a spinal implant device through a region that is densely packed with neural elements, muscle, ligaments, tendons and bone to access top surface 31 of inferior vertebra 30. In existing IF techniques, this requires extensive cutting and/or manipulation of this region, which can extend patient recovery time and subject the patient to other side effects, such as, for example, inflammation, which can be discomforting. Worse, in some patients, the patient must be entered in two or three of at least three possible body areas (i.e., the patient's posterior region in a posterior interbody fusion technique, the patient's anterior region in an anterior interbody fusion technique, the patient's lateral region in a lateral interbody fusion technique, and/or the patient's transforaminal region in a transforaminal interbody fusion technique) for the purpose of positioning the spinal implant device. More generally, existing IF techniques are substantially invasive and can be difficult to perform.
Further, a limitation of existing tools used in IF procedures relates to the design of the spinal implant device. In some IF procedures, locating the spinal implant device in the position of interest cannot be done by hand alone. Instead, a tool is required to push the spinal implant device to the position of interest, particularly when lordosis promotion is the goal of the IF procedure. Present spinal implant devices are configured so that their interface with the positioning tool occurs only along or parallel to the primary longitudinal axis, one of the orthogonal axes, of the spinal implant device. The primary longitudinal axis generally coincides with anterior or posterior directions of insertion. For example, certain presently used spinal implant devices are rectangular in shape and include a port that is centrally and parallelly aligned with the primary longitudinal axis of the spinal implant device used to releasably receive the positioning tool therein. As a result, such a spinal implant device (herein referred to as an “on-axis” spinal implant device) can only be moved and/or guided by the positioning tool in a straight line along its primary axis. If the on-axis spinal implant device is not initially aligned directly with its ultimate intervertebral location, or if it shifts during travel, it will not reach its ultimate position of interest without considerable effort and time to ensure that the on-axis spinal implant device is as close to the position of interest as possible. Even then, the surgeon can generally only approximate that position. Therefore, the configuration of current on-axis spinal implant devices limits a surgeon's ability to place the spinal implant device effectively.
What is needed, therefore, is a spinal implant apparatus and method of using the apparatus that enable a surgeon to easily, consistently, and effectively position a prosthetic intervertebral spacer substantially at the anterior region of an intervertebral disc space, i.e. between the cortical rims of adjacent vertebrae, with as minimal an impact on the patient as possible. Such an apparatus would decrease patient risk, speed recovery and substantially improve success rates in terms of restoration of normal spinal confirmation and neurological decompression.